Self-repairing nanocapsule hybrid cottonseed insulating oil and preparation method thereof

Abstract

The application relates to the technical field of high-voltage insulation materials, and particularly discloses a self-repairing nano-capsule hybrid cottonseed insulating oil and a preparation method thereof. The insulating oil comprises a cottonseed oil carrier, and 0.5-3wt% of microcapsules are dispersed in the carrier. The core layer of the microcapsules is composed of boron nitride nanosheets and epoxy fatty acid methyl ester, and the shell layer is a polyurethane-silicon dioxide hybrid material. The microcapsules are prepared by an electrostatic spraying-sol-gel method and are uniformly dispersed in the cottonseed oil-based insulating oil. When thermal pressure is generated by local discharge, the microcapsules are broken to release active substances, BNNS are directionally migrated to the discharge defect to form a conductive network to shunt energy, and the epoxy ester is in-situ polymerized under the induction of an electric field to fill microcracks. The application breaks through the limitation of traditional physical adsorption, realizes intelligent sensing-repairing integration, and has high repairing efficiency.

Description

Technical Field

[0001] This invention relates to the field of high-voltage insulation materials technology, specifically to a self-healing nanocapsule hybrid cottonseed insulating oil and its preparation method. Background Technology

[0002] Cottonseed oil, due to its high flash point (>300℃), biodegradability, and environmental friendliness, has become an important alternative to mineral oil and is widely used in high-voltage electrical equipment such as transformers. However, the problem of oil cracking caused by overheating due to partial discharge during equipment operation has not been fundamentally solved. The high-energy electrons and reactive free radicals generated by partial discharge (PD) trigger a chain reaction, causing the insulating oil to decompose into low-molecular-weight acids, carbonized particles, and gases, forming conductive channels and accelerating insulation failure.

[0003] CN120209917A discloses a method for preparing a modified self-extinguishing insulating oil with flame retardant and self-healing functions. This method involves adding modified hexagonal boron nitride, magnesium hydroxide nanomaterials, and a microcapsule repair agent to the insulating oil. This inhibits the formation and propagation of electric arcs, resulting in high insulation strength, high flame retardancy, and self-healing capabilities, thus extending the service life of the insulating oil. However, the microcapsule repair agent used in this technology is based on an ionic liquid, and its repair mechanism mainly relies on adjusting local conductivity or the chemical environment. This makes it difficult to effectively fill and repair physical microcracks caused by discharge. Furthermore, the microcapsule shell (urea-formaldehyde resin) has a high rupture trigger temperature (approximately 400°C), which may result in insufficient sensitivity under the thermal pressure conditions generated in the early stages of partial discharge, leading to a delayed repair time. In addition, the insulating oil matrix still contains mineral oil components, leaving room for improvement in its environmental performance. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a self-healing nanocapsule hybrid cottonseed insulating oil and its preparation method, enabling integrated intelligent damage sensing and repair. It utilizes fully bio-based cottonseed oil as a carrier, offering superior environmental friendliness; and incorporates core-shell microcapsules, with the core layer comprising boron nitride nanosheets and epoxy fatty acid methyl esters, and the shell layer being a polyurethane-silica hybrid material. These microcapsules can precisely rupture under relatively low thermal pressure (>120℃ or >5 kPa) generated by partial discharge, releasing epoxy fatty acid methyl esters that rapidly polymerize in situ under an electric field, structurally filling microcracks; simultaneously, the boron nitride nanosheets migrate to form a conductive network to divert energy. This achieves more sensitive, timely, and thorough structural repair of insulation damage.

[0005] This invention provides a self-healing nanocapsule hybrid cottonseed insulating oil, which includes a cottonseed oil carrier, in which 0.5-3 wt% microcapsules are dispersed. The core layer of the microcapsules is composed of boron nitride nanosheets and epoxy fatty acid methyl ester, and the shell layer is a polyurethane-silica hybrid material. The surface of the microcapsules is modified with sodium dodecylbenzenesulfonate.

[0006] Furthermore, in the core layer, the mass ratio of boron nitride nanosheets to epoxy fatty acid methyl ester is 1:2~4; the lateral dimension of the boron nitride nanosheets is 50-200 nm, and the thickness is ≤5 nm; the molecular weight of the epoxy fatty acid methyl ester is in the range of 400-600.

[0007] Furthermore, the shell thickness is 50-100 nm.

[0008] Furthermore, the carrier contains 1-2 wt% microcapsules.

[0009] This invention also relates to a method for preparing the self-healing nanocapsule hybrid cottonseed insulating oil, comprising the following steps:

[0010] S1. Boron nitride nanosheets are uniformly dispersed in epoxy fatty acid methyl ester to obtain a core layer mixture, and polyurethane prepolymer, tetraethyl orthosilicate and ammonia are mixed to prepare a shell layer sol.

[0011] S2. The core layer mixture and shell layer sol were injected into a coaxial electrostatic spraying device and sprayed into an acetic acid coagulation bath to synthesize microcapsules. The microcapsules were then immersed in sodium dodecylbenzenesulfonate solution for modification to obtain modified microcapsules.

[0012] S3. The modified microcapsules are added to the cottonseed oil carrier and dispersed evenly to obtain self-healing nanocapsule hybrid cottonseed insulating oil.

[0013] Furthermore, after the boron nitride nanosheets in S1 were added to the epoxy fatty acid methyl ester, they were ultrasonically treated for 30-60 minutes to mix and disperse them.

[0014] Furthermore, the mass ratio of polyurethane prepolymer, tetraethyl orthosilicate and ammonia in S1 is (4-6):1:(0.2-0.4); after mixing, hydrolysis and condensation are carried out for 1.5-3 hours to form a shell sol.

[0015] Furthermore, during the spraying process of the coaxial electrostatic spraying device in S2, the voltage is 15-25 kV, and the pH in the acetic acid coagulation bath is 3.5-4.5; during modification, the concentration of sodium dodecylbenzenesulfonate solution is 0.05-0.2 wt%, and the soaking time is 0.5-2 h.

[0016] Furthermore, when the modified microcapsules in S3 are mixed with the cottonseed oil carrier, the mixing temperature is 50-70℃ and the mixing time is 1.5-3 h.

[0017] The present invention has the following beneficial effects:

[0018] This invention addresses the degradation of insulating oil caused by partial discharge or overheating by designing core-shell microcapsules. The core layer is filled with boron nitride nanosheets (BNNS) and cottonseed oil-derived epoxy fatty acid methyl esters; the shell layer is a polyurethane-silica hybrid material. Both are prepared into microcapsules using an electrostatic spray-sol-gel method and uniformly dispersed in cottonseed oil-based insulating oil. Under a local electric field, the BNNS migrates directionally via dielectric force (at a rate of 5-9 μm / s), forming a microcapsule with a conductivity of 10. - A conductive network with a density of 3 S / m shunts over 70% of the discharge energy. Epoxy fatty acid methyl ester undergoes ring-opening polymerization within 10 seconds under electric field induction, filling microcracks (maximum filling rate 92%). In the shell structure, silica particles are covalently embedded in the polyurethane matrix, ensuring a strictly linear relationship between shell fracture strength and the thermo-pressure threshold (>5 kPa) (R²=0.98), guaranteeing precise rupture only under the thermo-pressure (>120℃ or >5 kPa) generated by partial discharge. The released active substance BNNS migrates directionally to the discharge defect to form a conductive network that shunts energy. Epoxy ester undergoes in-situ polymerization under electric field induction to fill microcracks, achieving integrated intelligent damage sensing and repair. After 100 partial discharge cycles, the breakdown voltage recovery rate is >95%, and the dielectric loss increment is <5%. After 200 cycles, it still maintains a recovery rate of >90%. Compared with traditional plant-based insulating oils, the breakdown voltage retention rate after 100 PD cycles is improved by over 300%, and the repair efficiency is >85% within an electric field range of 5-30 kV / mm.

[0019] The surface of the microcapsules of the present invention is also modified with sodium dodecylbenzenesulfonate (SDBS). After modification, the Zeta potential is ≤-35 mV, and there is no sedimentation after standing for 6 months (the sedimentation rate conforms to Stokes' law, and the viscosity of cottonseed oil μ=0.28 mPa•s); thus enabling it to be uniformly dispersed in insulating oil. Attached Figure Description

[0020] Figure 1 The flowcharts for the preparation of microcapsules and the self-repair mechanism in Examples 1-3 are shown below;

[0021] Figure 2 The effect of microcapsule addition amount on insulating oil performance in Example 3;

[0022] Figure 3 This illustrates the effect of BNNS size on migration rate in Example 2.

[0023] Figure 4 The effect of epoxy ester content on repair performance in Example 3;

[0024] Figure 5 This illustrates the relationship between the number of PD cycles and the performance of the insulating oil in Example 1.

[0025] Figure 6 This illustrates the long-term cycling performance degradation trend in Example 1.

[0026] Figure 7 Temperature adaptability analysis in Examples 3-6;

[0027] Figure 8 Accelerated aging stability (80°C) in Example 1;

[0028] Figure 9 The repair performance under different electric field intensities is shown in Examples 3-3;

[0029] Figure 10 The relationship between microcapsule size distribution and performance in Example 1;

[0030] Figure 11 This is a performance comparison between Example 1 and traditional vegetable insulating oil (after 100 PD cycles).

[0031] Figure 12 This illustrates the effect of microcapsule concentration on the repair effect in Example 3. Detailed Implementation

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials used in the following examples are commercially available products.

[0033] This invention provides a self-healing nanocapsule hybrid cottonseed insulating oil, which includes a cottonseed oil carrier in which 0.5-3 wt% microcapsules are dispersed. The core layer of the microcapsules is composed of boron nitride nanosheets and epoxy fatty acid methyl ester, and the shell layer is a polyurethane-silica hybrid material.

[0034] In some embodiments, the mass ratio of boron nitride nanosheets to epoxy fatty acid methyl ester in the core layer is 1:2~4; the lateral dimension of the boron nitride nanosheets is 50-200 nm and the thickness is ≤5 nm; the molecular weight of the epoxy fatty acid methyl ester is 400-600, it is derived from cottonseed oil, and it has excellent compatibility with cottonseed oil carrier.

[0035] In a preferred embodiment, the shell thickness is 50-100 nm. 10-30 nm silica particles are covalently embedded in the polyurethane matrix, ensuring a strictly linear relationship between the shell's fracture strength and the thermo-compression threshold (>5 kPa) (R²=0.98), guaranteeing precise rupture only under the thermo-compression generated by the PD (>120°C or >5 kPa).

[0036] In a preferred embodiment, 1-2 wt% of microcapsules are dispersed in the carrier. Addition amounts exceeding 3.0 wt% will lead to performance degradation due to aggregation effects.

[0037] In a preferred embodiment, the surface of the microcapsule is further modified with sodium dodecylbenzenesulfonate.

[0038] This invention also relates to a method for preparing the self-healing nanocapsule hybrid cottonseed insulating oil, such as... Figure 1 As shown, it includes the following steps:

[0039] S1. Boron nitride nanosheets are uniformly dispersed in epoxy fatty acid methyl ester to obtain a core-layer mixture. In a preferred embodiment, after adding the boron nitride nanosheets to the epoxy fatty acid methyl ester, the mixture is ultrasonically treated for 30-60 minutes to ensure uniform dispersion and prevent agglomeration of BNNS in the epoxy ester. During ultrasonic treatment, a 300-watt probe-type ultrasonic instrument is preferably used to continuously ultrasonicate the mixture for 40 minutes. Temperature control (using an ice bath) is crucial during ultrasonication to prevent prepolymerization reactions due to localized overheating of the epoxy ester. The ultimate goal is to obtain a stable core-layer mixture with uniformly dispersed BNNS. A shell sol is prepared by mixing polyurethane prepolymer, tetraethyl orthosilicate (TEOS), and ammonia water. The mixing is performed with magnetic stirring at room temperature. This process is a hydrolysis-condensation reaction, aiming to allow the silanol generated from the hydrolysis of TEOS to react with the polyurethane prepolymer, ultimately forming a transparent polyurethane-silica hybrid sol. This sol needs to possess good flowability and a certain degree of stability (gel time greater than 4 hours) for subsequent electrostatic spraying.

[0040] S2. The core-shell mixture and shell sol were separately injected into a coaxial electrostatic spraying device and sprayed into an acetic acid coagulation bath to solidify into microcapsules. The microcapsules were then immersed in a sodium dodecylbenzenesulfonate (SDBS) solution for modification, yielding modified microcapsules. The use of a coaxial electrostatic spraying device is a crucial step in the preparation of core-shell microcapsules. The core-shell mixture was loaded into the inner syringe, and its flow rate was precisely controlled. The shell-shell hybrid sol was loaded into the outer syringe, and its flow rate was controlled. A high-voltage electrostatic field was applied at the nozzle. Under the action of the high-voltage electrostatic field, the coaxial liquid flow was stretched and broken, forming tiny charged droplets that were ejected towards the receiving device. The receiving device contained an acetic acid aqueous solution (coagulation bath) with a pH adjusted to 4. When the shell sol droplets carrying the core material fell into the acidic coagulation bath, the shell sol rapidly gelled and solidified, encapsulating the internal core material, ultimately forming microcapsule particles with a core-shell structure. The solidification process took approximately 30 minutes. Afterward, the microcapsules were collected and washed with deionized water to remove residual acid. SDBS is a surfactant whose molecules adsorb onto the surface of microcapsules. After this process, the microcapsules are removed and vacuum dried. The zeta potential on the surface of the microcapsules is significantly reduced, which greatly enhances the dispersion stability and anti-settling ability of the microcapsules in the subsequent insulating oil, making them less prone to aggregation or precipitation.

[0041] S3. Add the modified microcapsules to the cottonseed oil carrier and disperse them evenly to obtain self-healing nanocapsule hybrid cottonseed insulating oil. According to design requirements, accurately weigh the modified microcapsules, and during dispersion, appropriately heat and mechanically mix them. This stirring process needs to provide sufficient shear force to ensure that the microcapsules can be uniformly and stably dispersed throughout the insulating oil system, avoiding excessively high local concentrations or sedimentation. After stirring, the particle size distribution of the microcapsules in the oil should meet the requirements (e.g., D90 ≤ 5 micrometers) to ensure the final performance of the product.

[0042] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0043] Comparative Example 1 (Traditional Plant-Based Insulating Oil Control)

[0044] It uses refined cottonseed oil without the addition of any microcapsules or nanomaterials.

[0045] Performance testing: Initial breakdown voltage 60 kV, tanδ 0.1%. After 100 PD cycles, the breakdown voltage dropped to 41.7 kV (recovery rate 69.5%), and tanδ increased to 0.83% (increment 0.73%).

[0046] Example 1 (Basic Example)

[0047] Core layer preparation: 0.5 g of boron nitride nanosheets (BNNS) with a transverse size of 150 nm were dispersed in 1.0 g of epoxy fatty acid methyl ester (mass ratio 1:2), and the mixture was treated with ultrasound (power 300 W) for 40 min to form a homogeneous core layer mixture.

[0048] Shell sol synthesis: 10 g of polyurethane prepolymer, 2 g of tetraethyl orthosilicate (TEOS) and 0.3 g of ammonia (25% by mass) were mixed and reacted at room temperature with magnetic stirring (500 rpm) for 2 h to form a transparent polyurethane-silica hybrid shell sol.

[0049] Microcapsule synthesis:

[0050] a. A coaxial electrostatic spraying device was used: the flow rate of the inner nozzle (core layer mixture) was set to 0.5 mL / h, and the flow rate of the outer nozzle (shell layer sol) was set to 1.5 mL / h;

[0051] b. The spray voltage is 20 kV, and the receiving distance from the nozzle to the receiving device is 15 cm;

[0052] c. The coagulation bath is an aqueous acetic acid solution with pH=4. After the droplets are injected, they solidify for 30 minutes to form core-shell microcapsules.

[0053] Surface modification: Microcapsules were collected and immersed in a 0.1 wt% sodium dodecylbenzenesulfonate (SDBS) aqueous solution for 1 h, followed by vacuum drying at 60 °C for 12 h to obtain surface-modified microcapsules. The zeta potential of the microcapsules was measured to be -42 mV, and the average particle size was 3.2 ± 0.8 μm.

[0054] Insulating oil compounding: Weigh 1.5 g of the above modified microcapsules (1.5 wt% of the total oil mass) and add them to 98.5 g of refined cottonseed oil (dielectric loss factor tanδ of 0.1%). Mix for 2 h at 60℃ and 700 rpm under mechanical stirring to ensure uniform dispersion of the microcapsules, thus obtaining self-repairing nanocapsule hybrid cottonseed insulating oil. The particle size distribution D90 of the dispersed microcapsules is 4.7 μm.

[0055] Performance testing:

[0056] a. The initial power frequency breakdown voltage was 60 kV. After 100 partial discharge (PD) cycles, the breakdown voltage was 57.3 kV, and the breakdown voltage recovery rate was 95.5%.

[0057] b. After 100 PD cycles, the dielectric loss factor (tanδ) increases by 0.18%;

[0058] c. The repair time for a single injury is approximately 25 seconds;

[0059] d. Accelerated aging tests (held at 80°C for 1000 hours) showed that the retention rate of microcapsules in oil was >98%, and the surface zeta potential decay was <8%;

[0060] e. Microcapsule particle size has a significant impact on performance: when D90 ≤ 5μm, the repair efficiency is >95%; when the particle size is >8μm, the repair efficiency drops to <80%. Example 2 (Study on the influence of BNNS transverse size)

[0061] To investigate the effect of BNNS size on self-healing performance, while keeping other conditions the same as in Example 1, such as core-to-layer mass ratio of 1:2 and microcapsule addition of 1.5 wt%, only the lateral size of BNNS was changed, and the following comparative experiments were conducted.

[0062] Example 2-1 (BNNS size: 50 nm)

[0063] Core layer preparation: 0.5 g of BNNS with a lateral dimension of 50 nm was dispersed in 1.0 g of epoxy fatty acid methyl ester. Due to the increased specific surface area of ​​BNNS, the ultrasonic dispersion time was extended to 50 min to ensure sufficient dispersion.

[0064] Performance testing:

[0065] a. The migration rate of BNNS under an electric field is approximately 9 μm / s;

[0066] b. After 100 PD cycles, the breakdown voltage is 57.0 kV, and the recovery rate is 95.0%;

[0067] c. The increment of tanδ is 0.20%.

[0068] Analysis: Smaller-sized BNNS have stronger migration capabilities, but are more prone to slight aggregation, which has a certain offsetting effect on the recovery of insulation performance.

[0069] Example 2-2 (BNNS size: 100 nm)

[0070] Core layer preparation: Take 0.5 g of BNNS with a transverse dimension of 100 nm, disperse it in 1.0 g of epoxy fatty acid methyl ester, and sonicate for 40 min.

[0071] Performance testing:

[0072] a. The migration rate of BNNS is approximately 7.5 μm / s;

[0073] b. After 100 PD cycles, the breakdown voltage is 57.8 kV, and the recovery rate is 96.3%;

[0074] c. The increment of tanδ is 0.16%.

[0075] Analysis: This size of BNNS achieves a good balance between migration rate and dispersion stability, demonstrating excellent overall repair performance.

[0076] Examples 2-3 (BNNS size: 80 nm)

[0077] Core layer preparation: Take 0.5 g of BNNS with a transverse dimension of 80 nm, disperse it in 1.0 g of epoxy fatty acid methyl ester, and sonicate for 40 min.

[0078] Performance testing:

[0079] a. The migration rate of BNNS is approximately 7 μm / s;

[0080] b. After 100 PD cycles, the breakdown voltage is 58.3 kV, and the recovery rate reaches 97.1%;

[0081] c. The increment of tanδ is 0.15%.

[0082] Analysis: 80 nm BNNS exhibits the best migration and network construction efficiency in this system, thus the electrical performance after repair is optimal.

[0083] Summary: As attached Figure 3 As shown, BNNS exhibits a clear structure-property relationship in the lateral dimension range of 50-150 nm. When the dimension is 80-100 nm, it achieves the best balance between high mobility and good dispersibility, obtaining the highest breakdown voltage recovery rate (>96%) and the lowest dielectric loss increment.

[0084] Example 3 (Study on the Influence of Core Layer Composition on Microcapsule Dosage)

[0085] This series of experiments systematically investigated the effects of core-to-layer mass ratio and microcapsule addition amount on performance. Except for specified variables, the BNNS size was 150 nm, and the basic procedures were the same as in Example 1.

[0086] Part 1: The Influence of Core-to-Main-Ratio (with corresponding appendix) Figure 4 )

[0087] The amount of microcapsules added was fixed at 1.5 wt%, while the mass ratio of BNNS to epoxidized fatty acid methyl esters was varied.

[0088] Example 3-1 (mass ratio 1:1)

[0089] Core layer preparation: BNNS 0.67 g, epoxy ester 0.67 g.

[0090] Performance testing: breakdown voltage recovery rate 91.8%, tanδ increment 0.25%, microcrack filling rate 78%, repair time 32s.

[0091] Analysis: Insufficient epoxy ester content and limited repair materials result in low filling rate, slow repair, and incomplete repair.

[0092] Example 1 (mass ratio 1:2)

[0093] Performance data: Breakdown voltage recovery rate 95.5%, tanδ increment 0.18%, fill rate 85%, repair time 25 s.

[0094] Example 3-2 (mass ratio 1:3)

[0095] Core layer preparation: BNNS 0.4 g, epoxy ester 1.2 g.

[0096] Performance testing: Breakdown voltage recovery rate 95.8%, tanδ increment 0.19%, fill rate 89%, repair time 21 s.

[0097] Analysis: Repair speed and thoroughness have been further optimized.

[0098] Example 3-3 (mass ratio 1:4)

[0099] Core layer preparation: BNNS 0.33 g, epoxy ester 1.32 g.

[0100] Performance testing: Breakdown voltage recovery rate 96.2%, tanδ increment 0.21%, fill rate 92%, repair time 18 s.

[0101] Analysis: The epoxy ester content is sufficient, the repair speed is fast and the filling is thorough, and the electrical performance recovery rate is high.

[0102] Comparative Example 3-1 (mass ratio 1:5)

[0103] Core layer preparation: BNNS 0.29 g, epoxy ester 1.45 g.

[0104] Performance testing: Breakdown voltage recovery rate 93.5%, tanδ increment 0.28%, fill rate 88%, repair time 20 s.

[0105] The effect of epoxy ester content on repair performance is shown in the figure. Figure 4 The relatively low content of BNNS results in insufficient energy conduction capacity, leading to an aggravated local thermal effect, a significant increase in tanδ, and impact on long-term stability.

[0106] Part Two: The Influence of Microcapsule Addition Amount

[0107] The mass ratio of BNNS to epoxidized fatty acid methyl ester in the core layer was fixed at 1:2, and the amount of microcapsules added to the insulating oil was varied.

[0108] Comparative Example 3-2 (addition amount 0 wt%, blank control, same as Comparative Example 1)

[0109] Performance testing: After 100 PD cycles, the breakdown voltage dropped to 41.7 kV (recovery rate 69.5%), with an tanδ increment of 0.73%.

[0110] Analysis: It lacks self-repair capabilities and its performance has deteriorated significantly.

[0111] Examples 3-4 (addition amount 0.5 wt%)

[0112] Performance testing: Breakdown voltage recovery rate 88.3%, tanδ increment 0.30%.

[0113] Analysis: It has basic repair capabilities, but its ability to deal with severe or multiple injuries is limited.

[0114] Examples 3-5 (addition amount 1.0 wt%)

[0115] Performance testing: Breakdown voltage recovery rate 93.1%, tanδ increment 0.22%.

[0116] Analysis: The repair effect is significantly improved.

[0117] Example 1 (addition amount 1.5 wt%)

[0118] Performance data: Breakdown voltage recovery rate 95.5%, tanδ increment 0.18%.

[0119] Examples 3-6 (addition amount 2.0 wt%)

[0120] Performance testing: Breakdown voltage recovery rate 96.0%, tanδ increment 0.17%.

[0121] Analysis: Repair performance has reached its peak.

[0122] Examples 3-7 (addition amount 3.0 wt%)

[0123] Performance testing: Breakdown voltage recovery rate 94.8%, tanδ increment 0.23%.

[0124] Analysis: Performance is good, but the increase in particle concentration begins to have a slight impact on dielectric loss.

[0125] Comparative Example 3-3 (4.0 wt%)

[0126] Performance testing: Breakdown voltage recovery rate 90.5%, tanδ increment 0.45%. Visible agglomerates were observed in the oil.

[0127] Analysis: Excessive microcapsules lead to severe aggregation, which disrupts insulation uniformity and degrades performance.

[0128] Comparative Examples 3-4 (5.0 wt%)

[0129] Performance testing: Breakdown voltage recovery rate 85.2%, tanδ increment 0.68%.

[0130] Analysis: Agglomeration effect intensifies, performance is now inferior to unmodified base oil.

[0131] summary:

[0132] The effect of microcapsule addition on insulating oil performance is shown in [reference needed]. Figure 2 The effect of microcapsule concentration on the repair effect is shown in [reference needed]. Figure 12 It can be seen that a core-to-layer mass ratio in the range of 1:2 to 1:4 achieves the best synergy between repair speed, thoroughness, and electrical stability. The microcapsule addition is effective in the range of 0.5-3.0 wt%, with 1.0-2.0 wt% being the optimal performance range. Too low a concentration results in insufficient repair capacity, while too high a concentration leads to performance degradation due to agglomeration. The effect of the number of partial discharge cycles on the performance of the modified insulating oil during performance testing in Example 1 is shown in [reference needed]. Figure 5As the number of PD cycles increases, the changing trends of key performance indicators such as the breakdown voltage recovery rate of the insulating oil and the increase in dielectric loss factor all verify the durability of the self-healing effect. Figure 6 This is a graph showing the long-term cycling performance degradation trend in Example 1. The graph reflects the degradation of the insulating oil breakdown voltage recovery rate after multiple PD cycles, used to assess long-term durability. Figure 8 This is an accelerated aging stability graph from Example 1. The graph records the changes in the insulating oil properties over time during an accelerated aging test at 80°C, used to assess thermal stability. Figure 10 This is a graph showing the relationship between microcapsule size distribution and performance in Example 1. The graph analyzes the influence of microcapsule particle size on repair performance, revealing the importance of particle size control. Figure 11 This is a performance comparison chart between Example 1 and traditional plant-based insulating oil. The chart compares the breakdown voltage retention rate and dielectric loss increment of the product of this invention with unmodified traditional plant-based insulating oil after 100 PD cycles, highlighting the superiority of this invention.

[0133] Figure 7 The breakdown voltage retention curves of the insulating oils prepared for Examples 3-6 (BNNS:epoxy ester mass ratio 1:2, microcapsule addition amount 2.0 wt%) at different temperatures show that they maintain more than 90% of the repair performance in the range of 20-100℃. Figure 9 The repair efficiency of the insulating oil prepared for Example 3-3 (BNNS:epoxy ester mass ratio 1:4, microcapsule addition amount 1.5 wt%) under different electric field strengths (5-30 kV / mm) showed that its repair efficiency was >85% in a wide electric field range.

[0134] The performance of the insulating oils prepared in the above examples and comparative examples is summarized in Table 1 (GB / T 507 "Determination of Breakdown Voltage of Insulating Oil").

[0135] Table 1. Performance indicators of insulating oils prepared in the examples and comparative examples

[0136]

[0137] Table 2 shows a comparison of the effects of the product prepared using Example 1 with traditional vegetable insulating oil (soybean oil) and commercially available nano-modified oil (silica nanoparticles doped with vegetable oil).

[0138] Table 2. Comparison of the effects of the product of this invention with traditional plant-based insulating oil and commercially available nano-modified oil.

[0139]

[0140] Based on the analysis of the data from the above embodiments and comparative examples, the self-healing nanocapsule hybrid cottonseed insulating oil prepared by this invention exhibits significant technical advantages. Its core-shell microcapsule design achieves precise rupture triggered by a thermo-pressurization threshold (>120℃ or >5 kPa), realizing a dual-functional synergy between BNNS conductive network construction and in-situ epoxy ester polymerization: BNNS migrate directionally to the discharge defect region at a rate of 5-7 μm / s driven by dielectrophoresis, forming a structure with a conductivity of up to 10. - The energy diversion channel of ³ S / m allows the synchronously released epoxy ester to complete ring-opening polymerization within 30 seconds under electric field induction, effectively filling microcracks (with a filling rate of up to 92%). Example data confirms that this synergistic mechanism enables the insulating oil to maintain a breakdown voltage recovery rate of over 95% after 100 partial discharge cycles, with the dielectric loss increment strictly controlled within 0.2%, reducing the performance degradation rate by more than 27 percentage points compared to unmodified cottonseed oil (control group).

[0141] In-depth analysis of the variables in the examples reveals that the fine-tuning of the microcapsule structure and composition plays a decisive role in performance improvement: based on Example 1, when the BNNS size is optimized to 80 nm (Examples 2-3), the migration rate increases by 40% compared to 150 nm, and the breakdown voltage recovery rate increases to 97.1%; while when the core epoxy ester ratio is increased to 4 times that of BNNS (Examples 3-3), the microcrack filling rate increases to 92%, and the repair time is shortened to 18 seconds. This clear quantification of structure-property relationships (e.g., the linear correlation between shell fracture strength and thermo-compression threshold R²=0.98) provides a reliable basis for the targeted optimization of the self-healing performance of insulating oil. Notably, the SDBS-modified microcapsules maintain a Zeta potential ≤-42 mV in cottonseed oil, and their dispersion stability strictly follows Stokes' law, ensuring no sedimentation under long-term static conditions, fundamentally solving the industry problem of secondary failure caused by nanomaterial aggregation.

[0142] In summary, this invention innovatively integrates damage sensing, energy conduction, and structural repair functions into a single core-shell system, establishing a new paradigm for adaptive protection of plant-based insulating oil. Its repair efficiency (<30 s per cycle), durability (performance degradation <5% after 100 PD cycles), and environmental adaptability (bio-based carrier + degradable components) provide a technical path with both theoretical innovation and engineering application value for the intelligent protection of high-voltage electrical equipment.

[0143] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A self-healing nanocapsule hybrid cottonseed insulating oil, characterized in that, The insulating oil comprises a cottonseed oil carrier, in which 0.5–3 wt% microcapsules are dispersed. The core layer of the microcapsules consists of boron nitride nanosheets and epoxy fatty acid methyl esters, with a mass ratio of boron nitride nanosheets to epoxy fatty acid methyl esters of 1:2–4. The lateral dimensions of the boron nitride nanosheets are 50–150 nm, and the epoxy fatty acid methyl esters are derived from cottonseed oil. The shell layer is a polyurethane-silica hybrid material. The surface of the microcapsules is modified with sodium dodecylbenzenesulfonate. The preparation of this insulating oil includes the following steps: S1. Boron nitride nanosheets are uniformly dispersed in epoxy fatty acid methyl ester to obtain a core layer mixture, and polyurethane prepolymer, tetraethyl orthosilicate and ammonia are mixed to prepare a shell layer sol. S2. The core layer mixture and shell layer sol were injected into a coaxial electrostatic spraying device and sprayed into an acetic acid coagulation bath to synthesize microcapsules. The microcapsules were then immersed in sodium dodecylbenzenesulfonate solution for modification to obtain modified microcapsules. S3. The modified microcapsules are added to the cottonseed oil carrier and dispersed evenly to obtain self-healing nanocapsule hybrid cottonseed insulating oil.

2. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: The thickness of the boron nitride nanosheets is ≤5 nm.

3. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: The shell thickness is 50-100nm.

4. The self-healing nanocapsule hybrid cottonseed insulating oil according to any one of claims 1 to 3, characterized in that: The carrier contains 1-2 wt% microcapsules.

5. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: After adding boron nitride nanosheets from S1 to epoxy fatty acid methyl ester, the mixture is ultrasonically treated for 30-60 min to achieve uniform dispersion.

6. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: The mass ratio of polyurethane prepolymer, tetraethyl orthosilicate and ammonia in S1 is (4-6):1:(0.2-0.4); after mixing, hydrolysis and condensation are carried out for 1.5-3 hours to form a shell sol.

7. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: When the coaxial electrostatic spray device in S2 is spraying, the voltage is 15-25 kV, and the pH in the acetic acid coagulation bath is 3.5-4.

5.

8. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: When modifying S2, the concentration of sodium dodecylbenzenesulfonate solution is 0.05-0.2 wt%, and the soaking time is 0.5-2 h.

9. The self-healing nanocapsule hybrid cottonseed insulating oil according to claim 1, characterized in that: When the modified microcapsules in S3 are mixed with cottonseed oil carrier, the mixing temperature is 50-70℃ and the mixing time is 1.5-3 h.

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